Electric safety-fuse.



R. C. COLE.

ELECTRIC SAFETY FUSE.

APPLICATION FILED APR.B, 1914.

Patented May 25, 1915.

* UNITED STATES PATENT OFFICE.

ROBERT 0, com cs nhnTronn, CONNECTICUT, 'AssIGNoR To THE JOHNS-PRATT COMPANY, or HARTFORD, CONNECTICUT, A CORPORATION or CONNECTICUT.

ELEcTRIo SAFETY-FUSE.

To all whom it may concern:

Be it known that I, ROBERT C. Come, a citizen of the United States, residing at Hartford, in the county of Hartford and State of Connecticut, have invented a new and useful Improvement in Electric Safety- Fuses, of which the following is a specification.

This invention relates to the construction of electric safety fuses which are designed to be used for protecting lines and apparatus in circuits in which the energy is great, such for instance, as six hundred vhlt-one thousand ampere circuits, and twenty-five hundred to sixty-six thousand volt circuits, but of course, it is to be understood that the invention herein set forth is not limited to circuits of the as examples.

Theobject of the invention is to produce a fuse which will operate surely and accurately at the\exact predetermined time without external manifestation, that is, without explosion or the emission of flame, when arparticular powers mentioned ranged in circuits of high pressure, and circuits of large quantity, and thus provide a simple, cheap and safe thermal protector which can be used to protect lines and apparatus from damage by accidental or abnormal conditions of currents having great energy. To attain this object the fusible conductor, of one or more'wires or strips,

that is connected between the interior terminals, is embedded within and closely surrounded on all sides, for a relatively short distance at the middle of the casing, with a levigated, amorphous, non-hygroscopic electrical non-conductor, such as rotten stone,

and the remainder of the casing, on each side of the middle section, is filled with a granular electrical non-conducting compound, such as plaster of Paris and whiting, having more air space between and moisture in the granules, and therefore having. greater heat absorbing, s condensing and pressure resisting quallties, althoughless electrical resistance, than the powder at the middle.

Dehydrated non-conducting infusorial earth ground to an impalpable powder, such as rotten stone, will remain a non-conductor under all of the conditions met in use in fuses placed in circuits carrying current of great ener and it has properties which, when a fus1 1e conductor-is disrupted with- Specification of Letters Patent. Patented May 25, 1915.

Application filed April 8, 1914. Serial No. 830,389. l

in it, even though the energy is great, tend to instantly quench a violent arc. However such a levigated amorphous substance owing to its lack of mechanical cohesion-its instability-and the lack of air space between the particles cannot be used to entirely fill the inclosing' case of a fuse siibjected to great energy because when the fusible conductor is disrupted under short circuit conditions the powder will not absorb and condense the gases generated but will yield and allow the circuit to form a path through it and thus conduce to a continuation of the destructive arc until the fusible conductor is consumed back to the interior terminals with disastrous results.

A granular compound, such as one formed of granulated calcined gypsum and calcium carbonate-plaster of Paris and whiting, has enough mechanical stability and sufficient air space in the interstices between the grains to resist dispersion and permit the rapid diffusion and condensation of the gases generated when the conductor fuses and consequently relieve the pressure, but if the casings of fuses subjected to great energy are completely filled with such com pounds the are which is formed on the disside and backing up sch an unstable substance with a granular compound of greater mechanical stability, although it may have less electrical resistance, "such as one formed of grains or pellets of plaster of Paris and whiting, I can utilize the high resistance arc-quenching qualities of the powdered earth and the absorbing and condensing qualities of the granular compound, and produce efficient fuses which will operate successfully without external ,manifestation when blown under both short circuit and g overload conditions of current having great energy. p

. Figure 1 of the accompanylng drawihgs shows a central longitudinal section of a fuse which embodies this invention. Fig. 2 shows a transverse section in the plane indicated by the dotted line 2-2 on Fig. 1. Fig. 8 shows a transverse section on the plane indicated by the dotted line 3'3 on Fig. 1.

The casing of the fuse shown is formed of a'tube of insulating material 1 thathas its ends closed by metallic caps 2. At the ends of the casing are the exterior conducting terminals 3, which are utilized to connect the fuse in the circuit, and the interior conducting terminals 4 to which the ends of the fusible link are connected. This link, in the form shown, is composed of a plural number of thin flat strips 5 of easily fusible metal, such as zinc. The number and shape of the strips and the method of connecting them with the interior terminals is immaterial to this invention.

A short section at the middle of the casing is filled with levigated, amorphous, infusorial earth 6, such as rotten stone. This substance has high electrical resistance and a very small percentage of moisture, and it remains in a very dry, non-hygroscopic condition. As a result of these characteristics, and its mechanical instability it acts, when disturbed by the blowing of the fuse,'to very efi'ectively snuff out or choke up the are. On each side ofthis dry impalpable powder the casing is filled with granular material 7. This material may be made by mixing plaster of Paris and whiting with water and after baking and drying this mixture, break ing it up into granules or pellets of the de sired size. This compound while having less electrical resistance and containing more moisture than the dry powder at the center, has greater mechanical coheslon and more air space between the granules, therefore it aids in retaining the mechanical stability of the arc quenching powder and provides for the difl'usi on and condensation of theigases. In a fuse constructed according to this invention, wlth a current of great energy, un-

der overload conditions the fusible strips open but a short distance in the 12; under short circuit conditions'the opening seldom extends beyond the ends of the sec tion of fine powder, the expansion of the gases into the lnterstices of the granular heat absorbing and condensing compound,

which is cooler than the powder, acting to inclosing case, interior and exterior conducting terminals at the ends of the case, a fusible conductor connecting the interior terminals, a levigated non-conductor surrounding the fusible conductor for a short distance in the case, anda granular non-conductor filling the remainder of the case each side of the levigated non-conductor.

2. An electric safety fuse consisting of an inclosing case, interior and exterior conducting terminals at the ends of the case, a fusible conductor connecting the interior terminals, a levigated non-conductor surrounding the fusible conductor at the middle of the case, and a granular compound filling the remainder of the case.

3. An electric safety fuse consisting of an inclosing case, interior andexterior conduct ing terminals at the ends ofthe case, ajfusif ble conductor connecting the interior terminals, a levigated amorpho'us infusorial earth v 4. An electric safety fuse consisting of an inclosing case, interior and exterior conducting terminals at the ends of the case, a fusible conductor connecting the interior terminals, aportion of the fusible conductor being surrounded by a dry amorphous non: conductor, andthe remainder of the fusible conductor being surrounded by a granular and more hygroscopic non-conductor.

5. An electric safety'fuse consisting of an inclosing case, interior and exterior conduct ingterminals at the ends of the case, a fusible conductor connecting the interior terminals, rotten stone surrounding a section of the fusible conductor at the middle of the case, and a granular compound of plaster of Paris and whitingsurrounding the remain- ,"Wider, and der of the case.

nonnnr 0. corn I Witnesses? H, G. BRAIN/inn, I Duncan (X Hooxnn. 

